In the petroleum industry, both for drilling operations and refining, pressurized fluids must be monitored continuously and temperatures below the freezing point of the flowing fluids are often encountered. The moving fluids resist freezing; however, the standing fluid in the lines to the monitoring gauges and in the gauges themselves often freeze since the fluid is essentially stationary. Various methods are employed to counteract this freezing in the standing lines. Heat strips are wrapped around the lines and gauges, warm water is sprayed on the lines and gauges, and other means are employed. Due to the high or low pressures that may be involved, e.g., from 10 PSI to 500 PSI, no satisfactory seal has previously been found which could separate the measured fluid from a non-freezing fluid which could be used in the standing line and monitoring gauge. The invention presented here eliminates these longstanding problems by providing a sealing piston which transmits the pressure variations of the measured fluid to a separate dissimilar fluid in the standing line and gauge which will not freeze at the temperatures encountered and will keep the two fluids substantially separated.
A bushing is provided which screws or other wise attaches to the pipe line, or a cut-off valve thereon, carrying the fluid to be monitored. This bushing is threaded on the inside to accommodate a piston cylinder. The piston cylinder is fitted into the bushing and a tight fitting piston made from any suitable material is slidably disposed within the cylinder. A thick walled pressure pipe with the end machined flat is screwed into the open end of the piston cylinder and provides a sealing surface against which the piston end may seat. The standing gauge pipe and gauge are filled with suitable non-freezing and lubricating fluid and sealed. The piston under pressure from the fluid to be monitored transmits the pressure to the fluid in the standing pipe and pressure gauge while substantially separating the two fluids at opposite ends of the piston. When there is no pressure in the monitored fluid pipe, the piston seats against the shoulder of the bushing to prevent the fluid in the standpipe and gauge from leaking.
In case of a break in the line between the piston and the gauge, the piston will prevent the leakage of fluid from the pipe line. Accordingly, the apparatus of the present invention serves also as a safety device.
In high temperature applications, the piston is provided with O-rings formed of Grafoil or the like that are disposed in circumferential bores near the ends thereof. Such O-rings can withstand temperatures up to 1,000.degree. F. and are particularly useful in nuclear power or fossil fuel plants.